Micro yaw rate sensors

Abstract

Yaw rate sensors are provided, the use of which permits quantitative measurement of yaw rate. The yaw rate sensor comprises at least a base, a first suspension and a second suspension with a proof mass supported between the two suspensions, which together form a resonator. The first suspension has a pair of thin-wire driving electrodes double side patterned on the surfaces. When a driving voltage is applied to the driving electrodes, it imposes an electric field to piezoelectrically induce a driving resonance. When the sensor is rotated around its sensing axis, the resonator will be forced to generate a sensing resonance out of the driving resonance plane to compensate the change in the linear momentum which must be conserved. The piezoelectric charge signal generated by the sensing resonance on the sensing electrodes which are double side patterned on the surfaces of the second suspension is used to detect the yaw rate. Specifically, the amplitude of the sensing resonance is in proportion to the yaw rate. The structure of the yaw rate sensors of this invention is suitable for mass production by lithographic micromachining techniques at low cost.

What is claimed is:  
     
         1 . A micro yaw rate sensor comprising: 
 a) a base substrate wafer made of piezoelectric material;    b) a pair of suspensions, namely a first suspension and a second suspension;    c) a proof mass connected to said base substrate by said first suspension and said second suspension from two opposite sides;    d) a plurality of driving electrodes disposed on top and bottom surfaces of said first suspension;    e) a plurality of sensing electrodes disposed on top and bottom surfaces of said second suspension;    wherein, an electric potential is impressed on said driving electrodes to excite a driving resonance within said substrate wafer plane, while occurrence of a sensing resonance caused by Coriolis force in direction out of said substrate wafer plane and perpendicular to said driving resonance is detected by electrical measurement from said sensing electrodes, and said sensing resonance is an indication of yaw rate.    
     
     
         2 . The micro yaw rate sensor of  claim 1 , wherein, said base substrate of piezoelectric material is a Z cut monocrystalline quartz wafer.  
     
     
         3 . The micro yaw rate sensor of  claim 2 , wherein, said suspensions and said proof mass are carved out from said base substrate by micro machining.  
     
     
         4 . The micro yaw rate sensor of  claim 3  wherein, said suspensions have multiple parallel beams to enhance said driving resonance.  
     
     
         5 . The micro yaw rate sensor of  claim 4 , wherein said driving electrodes are four thin wires being double side patterned, two at each side, along the centerlines and the edges of said first suspension in a serpentine manner, while said sensing electrodes are two straight lines being double side patterned, one at each side, along the edges on said second suspension.  
     
     
         6 . The micro yaw rate sensor of  claim 5 , wherein said driving electrodes at one side of said base substrate are connected with identical driving electrodes at another side.  
     
     
         7 . The micro yaw rate sensor of  claim 1 , wherein said first suspension and said second suspension are identical in structure and symmetrical to the center of the proof mass.  
     
     
         8 . The micro yaw rate sensor of  claim 2 , wherein, said suspensions are beams extended along the Y direction of said Z cut monocrystalline quartz wafer with rectangular cross section, and said driving resonance resonant in the X direction while said sensing resonance is in Z the direction of said Z cut monocrystalline quartz wafer.  
     
     
         9 . The micro yaw rate sensor of  claim 2 , wherein a plurality of sensing electrodes being patterned on top and bottom surfaces along the edges and the centerlines of said second suspension to monitor said driving resonance and to detect the acceleration in the X and Z directions of said Z cut monocrystalline quartz wafer.  
     
     
         10 . The micro yaw rate sensor of  claim 2 , further comprising: 
 f) an integrated circuit to perform said electric measurement and signal processing, and said integrated circuit further comprising: a) a driver module; b) a amplifier module; c) a bandpass filter module; and d) a demodulator module.    
     
     
         11 . The micro yaw rate sensor of  claim 10 , wherein said integrated circuit further comprising: e) a signal processing module to calculate the acceleration in the X and Z directions of said Z cut monocrystalline quartz wafer.  
     
     
         12 . The micro yaw rate sensor of  claim 2 , further comprising: 
 f) a Y beam cantilever with double side patterned thin-wire electrodes being disposed nearby the resonator on said Z cut monocrystalline quartz wafer to add an integrated two dimensional accelerometer in the X and Z directions of the quartz wafer to said sensor.    
     
     
         13 . The micro yaw rate sensor of  claim 1 , further comprising: 
 f) an identical second resonator which resonate at same frequency but in opposite direction with said resonator to offer better redundancy, accuracy, reliability and resistance to external shock and vibration.    
     
     
         14 . The micro yaw rate sensor of  claim 2 , wherein, said driving electrodes have also been disposed on said second suspension to achieve higher driving efficiency.  
     
     
         15 . The micro yaw rate sensor of  claim 2 , wherein, said sensing electrodes have also been disposed on said first suspension to achieve higher accuracy and redundancy.  
     
     
         16 . The micro yaw rate sensor of  claim 8  modified to operate with said sensing resonance as driving resonance, and said driving resonance as sensing resonance.  
     
     
         17 . The micro yaw rate sensor of  claim 2  simplified to combine two said suspensions and said proof mass into a single cantilever beam of rectangular cross-section, wherein said driving electrodes and sensing electrodes are all disposed on one single suspension beam.